GEN. SALIM IDRIS, convinced that the last stand of the Syrian Army in the long, grisly fight to control Aleppo will take place soon at the Academy of Military Engineering, dreads the moment.

It is not just the 2,000 or so well-armed soldiers holed up there, inside the square-kilometer campus on Aleppo’s eastern outskirts. Nor is it the reinforced concrete bunkers built under every building to withstand an Israeli air raid.

The toughest part for him is his fondness for both the officers in charge and the campus itself. When he defected in July 2012, General Idris, now chief of staff of the rebel forces, was a brigadier in the Syrian Army and dean of the academy after teaching there for 20 years.

“I cannot imagine that we will attack the academy,” General Idris said in a wide-ranging interview in a hotel cafe. “All the officers inside the academy are my colleagues. I don’t want to fight against them; I don’t want to see them killed or injured. I hope they leave before we attack.”

General Idris, 55, a stocky figure with a neatly trimmed mustache who was wearing a dark suit and tie, said he planned to deploy outside the academy when the fight begins, to make one last-ditch attempt to convince his old colleagues to defect.

“We cannot do anything about it if they don’t,” he said with a shrug.

Much of Syria’s future rests on General Idris’s success on the battlefield. Critics say the newly unified command structure he presides over lacks both the ground presence and the heavy weapons that are so desperately needed. Without both, they say, it will be impossible for him to forge a cohesive force from the thousands of fractious, fiercely independent rebel brigades arrayed against the still formidable military of President Bashar al-Assad.

UNDER intense pressure from Western and Arab backers, hundreds of Free Syrian Army commanders gathered in Turkey last December to select a 30-member Supreme Military Council, which in turn chose General Idris as chief of staff.

They unified, grudgingly, because they were promised heavy weapons, they said, in particular antiaircraft and antitank weapons, and other, nonlethal aid.

Some has materialized, although not nearly enough to transform the rebel effort, General Idris said. Secretary of State John Kerry this week pledged $60 million in additional nonlethal aid and training. The general stressed that the rebels need weapons and ammunition to fight the government, but would take anything they could get.

“The fighter also needs food and medical aid and care and cotton and bandages and sterilizers — the fighters need to live,” he said in a brief phone interview from northern Syria. “I was just visiting one of the military field hospitals. I swear that the situation there would make your heart bleed. The hospitals are so basic with very limited resources.”

Previous American aid seemed to amount to a trickle of small, odd lots. The Americans gave him nine ordinary black and gray Toyota pickup trucks, for example. General Idris kept three to move around with his staff and turned over the rest to field commanders. The communications equipment provided is too weak to reach across the country, he said, so he uses Skype. There were enough fatigues from the United States for 10,000 soldiers, which were nowhere near enough, given the roughly 300,000 rebel fighters, he said.

In addition to planned training efforts by the Americans, General Idris is urging Washington to train handpicked commando teams to help secure Syria’s suspected stock of chemical weapons if the government teeters. As for financial support, General Idris said very little had been forthcoming.

“We were promised a lot,” he said, “but when the moment of truth arrives they think a lot and give very little.”

General Idris and various aides say that some 70 percent to 80 percent of the field commanders are loyal to the joint military command, but other opposition leaders and rebel commanders say the number shrinks continuously because of the credibility gap created by the lack of a reliable weapons supply.

“He is excellent, well respected and well liked — he has a clean past,” said Emad ad-Din al-Rashid, an opposition leader in Istanbul. “But the problem is that the Supreme Military Council is not a good representative of the battalions on the ground.”

There is also no shortage of field commanders who say the council leaders are too identified with the Assad government and have too little battlefield experience. “He is a professor, not a soldier, “ said Abu Abdelrahman al-Suri, the pseudonym of a commander of Ahrar al-Sham, a jihadi fighting movement.

General Idris and his officers bristle at such criticism, rattling off their years of military training and pointing out that they defected at great personal risk.

Like many Syrian officers, General Idris joined the military to escape poverty. He was one of nine children raised by a farmer who grew grain in a hamlet called al-Mubarakiyah, near Qattinah Lake just south of Homs.

HE left in 1977; eventually spending six years training in East Germany, where in 1990 he earned a Ph.D. in wireless communications. At the academy, he taught digital electronic design. He married and had five children, but planned to retire to his village.

An attack in May 2012 on al-Mubarakiyah pushed him to defect. He called the generals he knew in the area, hoping to ward off the assault. None called back. The army killed three people and arrested 70, including his wife’s only brother. He has never been released.

When news of the attack reached Aleppo, General Idris pretended to his fellow officers that nothing was amiss. “I could not tell them that the army came and destroyed the village — they would have arrested me, accused me of being a traitor who supported the revolution.”

He had just poured his savings into building his dream retirement house. It was destroyed, too. “I had not sat in my house for even an hour,” he said wistfully.

General Idris, soft-spoken and humble compared with many military men, said he received hundreds of telephone calls daily, some angry, from commanders across Syria.

He dispatches what he can. But he described a mysterious system whereby unknown donors pay money to arms dealers within Syria. When he requisitions supplies, the black marketers fill the orders if the accounts are full. He can usually get the Kalashnikov bullets, rocket-propelled grenades and small mortars that he needs. But if the accounts are empty, he gets nothing.

Many rebel battalion commanders were civilians before the uprising. Having organized a brigade from men in their villages, they balk at taking orders and refuse to coordinate attacks.

“They want everything from the chief of staff — weapons, ammunition, money,” General Idris said. “But if you ask them what did you do with the ammunition and weapons, and how did you spend the money, well, they don’t like any commander to ask them what they are doing. But we cannot work in this way.”

General Idris said he could work with most of the Islamist factions fighting in Syria, putting their number at about 50 percent of the rebels. The exception was al-Nusra Front, blacklisted by the United States. He said that they were helpful in the fight — estimating that they had 3,000 men — but it was the only group he labeled extremist.

For security, General Idris rarely sleeps in the same place for two nights running. He takes the dangers he faces with a little black humor, interrupting the interview to call his wife “to tell her that I am still alive.”

Over all, General Idris said he thought the war was progressing well for the rebels. The government was resorting to tactics like long-range Scud missile attacks because it lacked soldiers, he said, but the rebels need the supplies promised by Western and Arab leaders more than ever.

“I would like to say to the decision makers in these countries, you cannot only listen to the news about Syria and watch the TV, to see the massacres and the destruction and wait,” he said. “If you still delay the decision to support Syria, you might take the decision when it is too late. Then Syria will be like Somalia.”

Hala Droubi contributed reporting.

A version of this article appears in print on , on Page A5 of the New York edition with the headline: Syrian Rebel Leader Deals With Ties to Other Side. Order Reprints | Today’s Paper | Subscribe